In the rich text editor:
@Sleepybun
In a comment:
[Sleepybun](https://chowlings.com/user/Sleepybun)
For Names and Avatars:
In the rich text editor:
%Sleepybun
In a comment:
[![Sleepybun's Avatar](https://chowlings.com/images/avatars/default.jpg)](https://chowlings.com/user/Sleepybun) [Sleepybun](https://chowlings.com/user/Sleepybun)